1. Field of the Invention
The invention relates to the preparation of Ru complexes with silicophilic ligands and to the use thereof as catalysts in transition metal-catalyzed hydrosilylation.
2. Description of the Related Art
The addition of Si—H-functional compounds onto compounds with aliphatic unsaturated bonds, especially C═C double bonds (hydrosilylation), has already been known for some time.
Hydrosilylation allows Si-containing organic compounds, organosilanes and organopolysiloxanes to be prepared. It is used especially in the addition-crosslinking curing of organopolysiloxanes in the silicone industry, for example for the production of elastomers, molding materials in the dental industry or antiadhesive coatings in the paper and films industry.
The catalysts used most frequently for the hydrosilylation reaction are platinum and its compounds, the platinum being used in metallic form, as metal fixed on an inorganic support, as a platinum salt or in the form of a soluble or insoluble platinum complex.
To date, for the majority of the hydrosilylation reactions performed industrially, the so-called “Karstedt catalyst” known from U.S. Pat. No. 3,715,334 and U.S. Pat. No. 3,775,452 is used, which consists predominantly of a dimeric platinum-tetramethyldivinylsiloxane complex, which can be described by the formula [Pt2(TMDVS)3] (TMDVS=tetramethyldivinyldisiloxane). The Karstedt catalyst is prepared proceeding from hexachloroplatinic acid H2PtCl6, which is likewise frequently used as a hydrosilylation catalyst in the form of an alcoholic solution.
Since platinum is one of the most expensive noble metals, there have already been frequent efforts to use other metals and compounds thereof as catalysts in hydrosilylation. For instance, the prior art already discloses the use of the other platinum group metals Pd, Rh, Ir, Ru in hydrosilylation. However, these have to date been described as alternatives to Pt in particular as catalysts for use in the case of specific substrates.
For example, US 2004/0092759 A1 and U.S. Pat. No. 5,559,264 describe Ru catalysts, for example RuCl3, RuBr3, Ru(acac)3, Ru/C, Ru3(CO)12, [RuCl2(CO)3]2, [Ru(COD)Cl2]n (COD=1,5-cyclo-octadiene), Ru(PPh3)2(CO)2Cl2 and Ru(PPh3)3(CO)H2 for the hydrosilylation of HSi(R)x(OR)3-x (x=0-2) with an olefinic halide, such as allyl chloride.
EP 0403706 A2 describes the use of Ru complexes with at least one tertiary phosphine ligand, for example Ru(CO)3(PPh3)2, RuCl2(PPh3)2, Ru(H)(Cl)(PPh3)3, Ru(PPh3)4H2 and Ru(CH2═CH2)(PPh3)3 as catalysts for the hydrosilylation of allylamines with SiH-functional silanes.
U.S. Pat. No. 5,248,802 describes the hydrosilylation of trichlorosilane with olefinic nitriles, for example acrylonitrile, in the presence of Ru-halogen or Ru-phosphine compounds, such as RuCl3, RuBr3, RuI3, Ru(CO)3(PPh3)2, RuCl2(PPh3)3, Ru(H)(Cl)(PPh3)3, RuH2(PPh3)4, Ru(CH2═CH2)(PPh3)3 and RuCl2(CO)2(PPh3)2.
Finally, DE 2810032 A1 describes the hydrosilylation of dichlorosilane with olefins in the presence of Ru complexes, for example RuCl2(PPh3)3, Ru(H)(Cl)(PPh3)3, RuH3(PPh3)3[Si(OMe)3], RuH3(PPh3)3[Si(OMe)2Ph] and RuH2(PPh3)4.
However, the use of other compounds with transition metals, such as Ni, Co or Fe, as catalysts for hydrosilylations has also already been described.
In general, these catalysts, however, are distinctly inferior to the common Pt catalysts with regard to reactivity and selectivity; especially for the crosslinking of polysiloxanes by means of a hydrosilylation reaction, the rate and selectivity of the non-Pt catalysts described to date for the hydrosilylation is generally insufficient. From an economic point of view too, these systems are usually not necessarily advantageous, since higher catalyst concentrations have to be employed for the non-platinum catalysts, and, in the case of rhodium, even higher costs than for platinum are to be expected.